U.S. patent application number 16/031688 was filed with the patent office on 2019-01-17 for ultrasonic capsule endoscopy device having image-based relative motion estimation.
The applicant listed for this patent is The Board of Trustees of the Leland Stanford Junior University. Invention is credited to Mohammad Amin Arbabian, Spyridon G. Baltsavias, Chienliu Chang, Jung Woo Choe, Arif Sanli Ergun, R. Brooke Jeffrey, JR., Butrus T. Khuri-Yakub, Farah Memon, Amin Nikoozadeh, Eric Olcott, Morten F. Rasmussen, Gerard Touma, Junyi Wang.
Application Number | 20190015070 16/031688 |
Document ID | / |
Family ID | 65000763 |
Filed Date | 2019-01-17 |
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United States Patent
Application |
20190015070 |
Kind Code |
A1 |
Memon; Farah ; et
al. |
January 17, 2019 |
Ultrasonic Capsule Endoscopy Device having Image-based Relative
Motion Estimation
Abstract
Improved localization of the capsule in acoustic capsule
endoscopy is provided by using analysis of the frames of the
acoustic images to deduce the relative motion of the capsule from
frame to frame. This idea can be supplemented with any combination
of: further localization methods; propulsion of the capsule via
acoustic radiation reaction; bidirectional communication and system
level feedback control; energy harvesting; photoacoustic (or x-ray
acoustic) imaging; and adding therapy and/or sensor capabilities to
the capsule.
Inventors: |
Memon; Farah; (Sunnyvale,
CA) ; Wang; Junyi; (Palo Alto, CA) ; Touma;
Gerard; (Stanford, CA) ; Baltsavias; Spyridon G.;
(Stanford, CA) ; Chang; Chienliu; (Palo Alto,
CA) ; Rasmussen; Morten F.; (San Francisco, CA)
; Arbabian; Mohammad Amin; (San Francisco, CA) ;
Khuri-Yakub; Butrus T.; (Palo Alto, CA) ; Jeffrey,
JR.; R. Brooke; (Los Altos Hills, CA) ; Nikoozadeh;
Amin; (San Carlos, CA) ; Choe; Jung Woo;
(Seoul, KR) ; Olcott; Eric; (Mountain View,
CA) ; Ergun; Arif Sanli; (Palo Alto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Board of Trustees of the Leland Stanford Junior
University |
Palo Alto |
CA |
US |
|
|
Family ID: |
65000763 |
Appl. No.: |
16/031688 |
Filed: |
July 10, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62531295 |
Jul 11, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 1/00016 20130101;
G01S 15/899 20130101; A61B 8/56 20130101; A61B 1/00029 20130101;
G06T 2207/10068 20130101; G06T 2207/10116 20130101; A61B 5/065
20130101; G06T 7/74 20170101; A61B 5/061 20130101; G01S 15/89
20130101; A61B 1/00034 20130101; A61B 5/0095 20130101; A61B 8/488
20130101; G01S 15/892 20130101; A61B 8/0841 20130101; A61B 1/041
20130101; G06T 7/73 20170101; A61B 8/54 20130101; A61B 2560/0242
20130101; G06T 2207/30028 20130101; A61B 8/12 20130101; A61B 8/5223
20130101; G01S 15/66 20130101; A61B 1/00156 20130101; A61B 10/0045
20130101; G01S 15/8997 20130101; A61B 5/073 20130101; A61B 5/6861
20130101; G06T 2207/10132 20130101; A61B 8/4254 20130101; A61B
8/4263 20130101; A61N 7/022 20130101; A61B 1/00009 20130101; G06T
2207/30244 20130101; A61B 1/0016 20130101; A61B 6/4057 20130101;
A61B 8/4416 20130101; A61M 31/002 20130101; A61B 2010/0061
20130101 |
International
Class: |
A61B 8/12 20060101
A61B008/12; A61B 8/00 20060101 A61B008/00; A61B 8/08 20060101
A61B008/08; A61B 5/00 20060101 A61B005/00; A61B 10/00 20060101
A61B010/00; G06T 7/73 20060101 G06T007/73; A61B 6/00 20060101
A61B006/00; A61M 31/00 20060101 A61M031/00; A61N 7/02 20060101
A61N007/02 |
Claims
1. Apparatus comprising: a capsule configured to be swallowed by a
patient; at least one diagnostic acoustic transducer array disposed
on the capsule and configured to be operational while the capsule
is ingested by the patient to provide acoustic images; a relative
location tracking subsystem configured to determine changes in
relative location and/or orientation of the capsule from one frame
of the acoustic images to another frame of the acoustic images
using an image processing method applied to the acoustic
images.
2. The apparatus of claim 1, wherein the image processing method is
selected from the group consisting of: local cross-correlation,
speckle tracking, Doppler estimation, and transverse oscillation
method.
3. The apparatus of claim 1, wherein the capsule is configured to
be self-propelled while ingested by an acoustic radiation reaction
force on the capsule due to emission of acoustic energy by the
capsule.
4. The apparatus of claim 1, wherein the apparatus is configured to
provide a synthetic acoustic image reconstruction from two or more
selected frames of the acoustic images combined with relative
location and orientation of the capsule from each of the selected
frames.
5. The apparatus of claim 1, wherein the apparatus is further
configured to provide absolute location tracking.
6. The apparatus of claim 5, wherein the absolute location tracking
employs one or more anatomical landmarks as location
references.
7. The apparatus of claim 5, further comprising one or more
acoustic transmitters disposed outside the patient, wherein the
absolute location tracking includes determining a location of the
capsule based on signals received from the acoustic transmitters at
the capsule.
8. The apparatus of claim 5, further comprising one or more
acoustic receivers disposed outside the patient, wherein the
absolute location tracking includes determining a location of the
capsule based on signals received from the capsule at the acoustic
receivers.
9. The apparatus of claim 5, further comprising at least one
localization acoustic transducer array disposed on the capsule and
configured to be operational while the capsule is ingested by the
patient to provide data for the absolute location tracking.
10. The apparatus of claim 5, wherein the at least one diagnostic
acoustic transducer array is configured as a dual-use array further
configured to be operational while the capsule is ingested by the
patient to provide data for the absolute location tracking.
11. The apparatus of claim 1, wherein the capsule is configured to
be powered while ingested by energy harvesting.
12. The apparatus of claim 1, further comprising an optical source
disposed on the capsule, wherein the at least one diagnostic
acoustic transducer array is configured to provide photoacoustic
imaging of acoustic radiation generated in the patient by
absorption of light from the optical source.
13. The apparatus of claim 1, further comprising an X-ray emitting
source disposed on the capsule, wherein at least one diagnostic
acoustic transducer array is configured to provide x-ray acoustic
imaging of acoustic radiation generated in the patient by
absorption of X-rays.
14. The apparatus of claim 1, further comprising a therapy module
disposed on the capsule and configured to provide a targeted
therapy selected from the group consisting of: high intensity
focused ultrasound and drug delivery.
15. The apparatus of claim 1, further comprising a sensor/sampling
module disposed on the capsule and configured to provide a
functionality selected from the group consisting of: fluid
sampling, tissue sampling, and ambient environmental sensing.
16. The apparatus of claim 1, further comprising a feedback control
system configured to control one or more operational parameters of
the capsule.
17. The apparatus of claim 1, further comprising an acoustic and/or
wireless electromagnetic bidirectional communication link between
the capsule and a component external to the patient.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. provisional
patent application 62/531,295, filed on Jul. 11, 2017, and hereby
incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to acoustic capsule endoscopy.
BACKGROUND
[0003] Currently, thorough examination of the digestive system is
available using endoscopic ultrasound (EUS), computed tomography
(CT), and magnetic resonance imaging (MRI). These techniques are
either harmful (CT imposes radiation), uncomfortable (EUS requires
sedation and insertion of catheter) or very expensive.
SUMMARY
[0004] The capsule ultrasound (CUS) device described herein can be
a low-cost, disposable, and ingestible capsule with an ultrasound
array attached to its body. After being swallowed by the patient,
this capsule can allow the doctors to seamlessly examine the entire
gastrointestinal (GI) tract, primarily the small intestine. The
ultrasound can be used to locate abdominal disorders and lesions,
find the GI wall thickness, and examine adjacent organs (such as
the pancreas). To make the CUS device a more feasible alternative
to aforementioned techniques, we describe additional features
beyond conventional ultrasound imaging, such as localization and
propulsion of the capsule.
[0005] An example of how these features and others are integrated
follows: the interior of the capsule contains the imaging (plus
localization, propulsion and/or energy harvesting in some
embodiments) electronics that control the ultrasound transducers,
power management electronics that control power distribution from
battery/storage element (and harvesting transducers in some
embodiments) to the rest of the electronics, battery/storage
element, memory circuitry to temporarily store image/localization
data, and wireless transceiver for wireless communication. In some
embodiments the interior of the capsule also contains reservoir(s)
for storing tissue/liquid samples or prepackaged drugs for drug
delivery, and/or optical/X-ray transducers for photoacoustic or
X-ray acoustic imaging. The abovementioned elements can be on
different printed circuit (PC) boards, connected to each other via
flexible substrate boards, or several components can be combined on
one or more boards. The exterior of the capsule may include
ultrasound transducers (for imaging, localization, propulsion
and/or energy harvesting, depending on specific embodiment), RF
antenna for wireless communication and pH electrodes/gas/pressure
sensor in some embodiments. In some embodiments some of the
abovementioned exterior elements such as the RF antenna can reside
in the interior instead.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIGS. 1A-B schematically show an embodiment of the
invention.
[0007] FIGS. 2A-B show exemplary capsule configurations.
[0008] FIGS. 3A-B show further exemplary capsule
configurations.
[0009] FIGS. 3C-D show field of view geometry for the capsule.
[0010] FIGS. 4A-B schematically show how several kinds of capsule
motion would affect the acoustic images.
[0011] FIG. 5 schematically shows use of an anatomical landmark as
a location reference.
[0012] FIGS. 6A-B show exemplary localization methods.
[0013] FIG. 7A schematically shows capsule propulsion using
acoustic radiation reaction.
[0014] FIGS. 7B-G show examples of acoustic capsule propulsion.
[0015] FIGS. 8A-B schematically show exemplary communication and
control for acoustic capsule endoscopy.
[0016] FIG. 9 shows harvesting externally provided acoustic energy
with the capsule.
[0017] FIG. 10 shows photoacoustic or x-ray acoustic imaging by the
capsule.
[0018] FIG. 11 shows addition of further capabilities to the
capsule.
DETAILED DESCRIPTION
[0019] In this description, several features of preferred
embodiments are described. Embodiments of the invention can include
these features individually or in any combination. The main topics
in the following description are 1) relative localization, 2)
absolute localization, 3) propulsion, 4) communication and control,
5) energy harvesting, 6) photoacoustic or x-ray acoustic imaging,
and 7) further options and variations.
1) Relative Localization
[0020] While traveling inside a patient's gastrointestinal tract,
the location of the capsule is important information for both
disease diagnostics and capsule adaptive control. After the capsule
ultrasound device captures images of the distinct layers of the
small intestine as well images of the neighboring organs, it is
important to acquire the location related to the images, in order
to locate a specific feature, like a tumor or cyst, determine the
capsule trajectory along the gastrointestinal tract, and possibly
to reconstruct 3D images or a full reconstruction of the
gastrointestinal tract. The location information can also serve as
feedback information for an external device to control the
operation mode and the frame rate of the capsule through
bi-directional wireless communication.
[0021] It is helpful to distinguish between relative localization,
which is identification of location changes of the capsule based on
analysis of the acoustic images obtained, and absolute
localization, which is identification of the position of the
capsule based on comparison to external position references. We
first consider relative localization.
[0022] Frame-to-frame tissue movement estimation can be used to
estimate and track the CUS device location and orientation as it
traverses the gastrointestinal tract. FIGS. 1A-B schematically show
the concept. Here FIG. 1A shows capsule 102 in GI tract 104. FIG.
1B shows how an acoustic field of view 106 can change to a new
field of view 108 as the capsule moves. Since these fields of view
will overlap (e.g., as shown) for typical system acoustic frame
rates and capsule speeds, analysis of the acoustic images in
relative location tracking subsystem 110 can provide relative
motion information.
[0023] FIG. 2A is an enlarged view of an exemplary capsule 102. In
this example, capsule 102 includes a cylindrical acoustic
transducer array 202 disposed around the circumference of the
capsule, along with one or several linear acoustic transducer
arrays 204 disposed along the length of the capsule. Such linear
transducer arrays are also referred to as `flat` acoustic
transducer arrays. This configuration allows the capsule to acquire
acoustic images which are orthogonal to each other. As a result,
translation in all three directions (x, y, and z-dimension) as well
as rotation around all axes (x and y and z) can be calculated by
cross-correlating successive images from the cylindrical and the
linear arrays. This helps to track the CUS device as it propagates
down the gastrointestinal tract. The frame-to-frame movement can be
estimated by many different techniques, such as: local
cross-correlation, speckle tracking, Doppler estimation,
transverse-oscillation-method, etc.
[0024] Accordingly, an exemplary embodiment of the invention is an
apparatus that includes a capsule configured to be swallowed by a
patient. The capsule includes at least one diagnostic acoustic
transducer array disposed on the capsule and configured to be
operational while the capsule is ingested by the patient to provide
acoustic images. The apparatus includes a relative location
tracking subsystem configured to determine changes in relative
location and/or orientation of the capsule from one frame of the
acoustic images to another frame of the acoustic images using an
image processing method applied to the acoustic images
[0025] The apparatus can be configured to provide a synthetic
acoustic image reconstruction from two or more selected frames of
the acoustic images combined with relative location and orientation
of the capsule from each of the selected frames. This is analogous
to synthetic aperture radar. More specifically, as the capsule is
moving through the GI tract, multiple datasets, each from a new
capsule position can be acquired. These datasets can be gathered
from the cylindrical array and the linear array. After knowing the
position of the capsule and the elements, using localization
techniques, these datasets can be synthetically focused to increase
both resolution and contrast in the resulting images. The synthetic
focusing technique could also be used to create a full 3D image of
a region of interest.
[0026] As described in greater detail below, this relative
localization can be supplemented with absolute localization. In
such cases, the acoustic transducer arrays on the capsule can be
dual-use arrays that provide data for both imaging and the absolute
location tracking, or separate location and imaging arrays can be
used. FIG. 2B shows an example of the latter approach, where 210
and 212 are imaging and localization cylindrical transducer arrays,
respectively. Similarly, 214 and 216 are localization and imaging
linear transducer arrays.
[0027] FIGS. 3A and 3B show two examples of capsules. FIG. 3A is a
3-D view of the example of FIG. 2A. FIG. 3B differs from the
example of FIG. 3A in that the cylindrical transducer array 202 is
disposed at the midline of the capsule, with linear acoustic arrays
disposed both above and below this midline. FIGS. 3C-D
schematically show the fields of view of the respective transducer
arrays. Here the z-axis is taken to be along the axis of the
capsule, which means that the image plane 320 of the cylindrical
transducer array will be in the xy plane. The linear transducer
arrays will have image planes parallel to the z axis, and one such
image plane is shown as 310 on FIG. 3D.
[0028] FIG. 4A schematically shows how a translation in the z
and/or x directions or a rotation about the y axis can be estimated
by comparing two or more acquired xz frames from the linear array.
The coordinate axes 402 apply to all sample images 404, 406, 408,
410, and are also consistent with the coordinates of FIG. 3D.
[0029] Here 404 is an initial image in the xz plane from one flat
array. 406 is a first example of a following image from the flat
array in the xz plane. Linear translation in the x direction can be
estimated by comparing the initial and the following images from
the flat array. 408 is a second example of a following image from
the flat array in the xz plane. Linear translation in the z
direction can be estimated by comparing the initial and the
following images from the flat array. 410 is a third example of a
following image from the flat array in the xz plane. Rotation
around the y axis can be estimated by comparing the initial and the
following images from the flat array.
[0030] FIG. 4B schematically shows how a translation in the x
and/or y directions or a rotation about the z axis can be estimated
by comparing two or more acquired xy frames from the cylindrical
array. Here the coordinate axes 412 apply to all sample images 414,
416, 418, 420, and are also consistent with the coordinates of FIG.
3D. For all sample images the inner central circle indicates the
boundary of the cylindrical array and the outer circle indicates
the boundary of the image.
[0031] Here 414 is an initial image in the xy plane from the
cylindrical array. 416 is a first example of a following image from
the cylindrical array in the xy plane. Linear translation in the x
direction can be estimated by comparing the initial and the
following images from the cylindrical array. 418 is a second
example of a following image from the cylindrical array in the xy
plane. Linear translation in the y direction can be estimated by
comparing the initial and the following images from the cylindrical
array. 420 is a third example of a following image from the
cylindrical array in the xy plane. Rotation around the z axis can
be estimated by comparing the initial and the following images from
the flat array.
2) Absolute Localization
[0032] In other approaches for absolute localization, to determine
the location of an in-vivo device, extra or external transducers
(i.e. magnetic transducers) are used. These methods usually require
the patients to wear external devices serving as frame coordinates,
or require the patients to keep stable near a bulky instrument.
These methods not only require extra devices, but also cause
inconvenience for the patients. In order to eliminate these extra
or external devices, we provide an ultrasonic image-guided
localization and registration method, so that the location of the
ultrasonic capsule could be automatically determined from the
ultrasonic image generated by the capsule itself.
[0033] In addition, the location can also serve as feedback
information to an external receiver and control device, and then,
based on the location of the capsule, the external device could
control the frame rate, propulsion direction and other operation
mode through the two-way communication.
[0034] Automatic localization can be accomplished by imaging the
anatomical landmarks, such as distant organs, using a cylindrical
transducer array encircling around the capsule, as well as one or
multiple flat linear transducer arrays along the axis direction of
the capsule, as shown in FIG. 3A-B. The transducer arrays used for
localization will work at modes different from the arrays used for
diagnostics. The diagnostic-mode arrays require a higher frequency
and better image resolution. For localization purpose, the arrays
will work at localization mode, which requires a lower frequency
and larger penetration depth. FIG. 5 schematically shows this
concept, where 502 is the anatomical landmark.
[0035] The cylindrical transducer array and the flat linear
transducer arrays along the long axis direction of the capsule have
a penetration depth of up to 10 cm. The images generated by these
transducer arrays would show anatomical landmarks around the GI
tract, therefore, by calculating the relative distance to the
anatomical landmarks according to the captured image, the location
of the capsule device can be determined as it travels the digestive
system. Meanwhile, because the 360 degrees ultrasound scans of the
cylindrical transducer array always start from the same elements,
these ultrasound images can provide information of the capsule
rotation around its axis. The linear transducer arrays can generate
images at a higher frame rate and the images can be used to trace
the capsule movement. Because of the high frame rate, the
peristalsis movement can be traced correctly. As indicated above, a
cross-correlation method can be used to calculate the relative
movement between two successive images captured by the same
transducer array, so that we can trace the capsule rotation using
the images acquired by the cylindrical array and calculate the
longitudinal capsule movement using the images of the flat arrays.
Based on the capsule rotation and movement, the image registration
can be performed by reconstructing the images into the same
coordinate system, so that the 3D image along the GI tract can be
eventually reconstructed.
[0036] Localization can also be accomplished using another
technique that involves putting several external airborne
ultrasound transducers in the room where the patient stays (such as
the on the chairs, on the bed, on the wall) and carry out
trilateration. FIG. 6A shows an example, where 602, 604, 606, 608
are the external transducers operating in receive mode. These
transducers will operate in the receive mode at a low frequency
(i.e., 100 kHz) and listen to the ultrasound signals emitted by the
corresponding low frequency transducers in the capsule. Knowing the
time of the emission of the signal by the transducers in the
capsule and the time of pulse detection by the transducers located
outside of the body, the time-of-flight algorithm can be used to
determine the location of the capsule inside the body. Or in the
opposite way, the transducers located outside the body can be used
as transmitters and the received signals by the transducer on the
capsule is used to localize the capsule inside the body, using
various algorithms such as how global positioning system (GPS)
works. FIG. 6B shows an example, where 612, 614, 616, 618 are the
external transducers operating in receive mode.
[0037] The RF antenna and external receiver device, as described in
greater detail below, can also contribute time-of-flight
information, which can improve the accuracy of the capsule location
calculation. This RF system can contain a pulsed-based duty-cycled
transmitter running at one or more frequencies. Time of flight and
trilateration techniques can be used to locate the transmitter
(capsule) with respect to an array (3 or more) of external
receivers. A differential time of flight method could also be used.
Here, multiple transmitters (two or more) on two sides of the
capsule transmit short RF pulses. The difference in time of arrival
can be used to locate the capsule. The RF frequency will be
selected as a compromise between tissue losses and antenna
efficiency (leading to SNR constraints) vs. D-TOF accuracy. In all
these systems the preferred pulse width resides in the 100 ps to 10
ns range. Chemical environment information (e.g. pH) acquired by
additional sensors could serve as another indicator for
localization.
3) Propulsion
[0038] During wireless capsule endoscopy, the capsule typically
travels in the GI tract passively via peristalsis. This imposes
several limitations on the imaging performance of the capsule, as
well as its capabilities to perform other medical tasks such as
drug delivery and biopsy. These limitations include: Higher
percentage of missed findings in the screening/diagnosing process;
Inability to stabilize the capsule to allow for treatment delivery;
Inability to direct the capsule toward areas of interest (e.g.
pathologies) to acquire images, treatment delivery, biopsy, etc.;
and Lower effective field of view.
[0039] The ability to propel the capsule inside the GI tract
provides several benefits that could allow exploring new features
and new capabilities. The ability to stabilize the capsule in the
GI tract improves its diagnostic and therapeutic capabilities by
allowing one to control the number of acquired images of the same
area of interest.
[0040] Propulsion could also be used to position and orient the
capsule in such a way to enable imaging specific internal organs
with either ultrasound imaging, photo-acoustic imaging, X-ray
acoustic imaging, or any other imaging modality. Another benefit is
to provide the capsule with adaptability to the different anatomies
of the various organs in the GI tract.
[0041] Propulsion can also help in revisiting certain locations of
abnormalities, and to control the duration the capsule stays inside
the GI tract. This can help control the energy consumed, and the
examination time.
[0042] To propel the capsule in the GI tract, the transducer array
can be wrapped around the capsule to generate ultrasonic waves that
can drive the capsule in any desired direction. In one
implementation, the array can be used as an interdigital transducer
(IDT) to generate surface acoustic waves (SAW). The direction of
these waves is such that it opposes the desired direction of
propulsion, and their acoustic pressure dictates the speed at which
the capsule travels. Another implementation uses the transducer
array as a phased array. To propel in a particular direction, a
subset of the array elements generates a focused ultrasound beam in
the opposite direction. A subset of transducer elements can
generate focused ultrasound beams with variable directivity, and
intensity.
[0043] More specifically, the propulsion concept considered here is
that capsule be self-propelled while ingested by an acoustic
radiation reaction force on the capsule due to emission of acoustic
energy by the capsule. FIG. 7A shows this concept. Here 102 is the
capsule, 702 is the acoustic transducer, 704 is emitted acoustic
radiation and 706 is the radiation reaction force on the capsule.
As suggested by FIG. 7A, the reaction force is generally in the
opposite direction to any directional acoustic radiation. Note that
this radiation reaction force does not depend on how the contents
of the GI tract move in response to the acoustic radiation, in
contrast to other approaches where the induced flow of GI tract
contents is the propulsion mechanism.
[0044] FIGS. 7B and 7C schematically show propulsion of capsule 102
backward relative to a peristalsis 712 for the phased array and IDT
cases respectively. Here the net motion 716 is the superposition of
peristalsis 712 and radiation reaction 714. Similarly, FIGS. 7D and
7E schematically show propulsion of capsule 102 forward relative to
peristalsis 712 for the phased array and IDT cases respectively.
Here the net motion 724 is the superposition of peristalsis 712 and
radiation reaction 722. FIG. 7F shows how capsule 102 can be
rotated about its midline by radiation reaction forces. FIG. 7G
(which is an end view) shows how capsule 102 can be rotated about
its axis by radiation reaction forces.
[0045] In addition to propelling the capsule backward, forward, or
in any direction that changes its current location, the capsule can
also be rotated in both directions around its axis. This, for
example, can help improve the resolution of the acquired images by
rotating the capsule by a distance smaller than the transducer
elements pitch, which effectively provides higher resolution.
Another benefit of rotating the capsule around its axis is to
create better contact with the surrounding tissue/organ.
[0046] Acoustic propulsion provides significant advantages compared
to conventional propulsion approaches. Several capsule designs use
magnetic fields to rotate the capsule and translate its location by
applying an external magnetic field that interacts with another
metal or magnetic body placed inside the capsule body. This
requires extra area, external requirement, and of course, external
monitoring. Several other implementations rely on using robotic
parts to control the position of the capsule and push it in a
particular direction. These types of implementations are highly
invasive, consume a lot of power, are complex to design, and
require a large additional area. Another implementation uses
electrodes to electrically stimulate the organ wall and cause it to
contract. This emulates the effect of peristalsis, and therefore
pushes the capsule forward. This technique is highly invasive as
well.
[0047] Compared to the current implementations, the design of this
work is non-invasive. It uses acoustic signals to propel the
capsule, without requiring any contact with the biological tissue.
This implementation also does not require any additional parts
attached to the capsule, and no external devices. This reduces the
design complexity since the imaging transducer array that is
already wrapped around the capsule can also be used for propulsion,
and does not require any contact with the surrounding tissue which
can typically cause contaminations, and other unwanted effects.
4) Communication and Control
[0048] FIG. 8A schematically shows closed loop control of capsule
102. Here controller 802 is in bidirectional communication with
capsule 102. This link can be an acoustic link and/or a wireless
electromagnetic link, as described in more detail below. With such
a link in place, feedback control can be used to control one or
more operational parameters of the capsule. FIG. 8B shows some
further details relating to such configurations. Here input block
804 is part of the user interface and includes items such as user
input (both patient and medical professional), desired capsule
location, desired capsule mode of operation (e.g., `enhanced
imaging mode`), etc. Input block 806 is the uplink from the
capsule, and can include parameters such as capsule orientation
(pitch, roll, yaw), location, velocity, pressure, system status,
remaining energy, etc. Output block 808 is the downlink to the
capsule, and can include parameters such as propulsion force
(magnitude and direction), image focus depth, image frame rate,
etc. Output block 810 is part of the use interface and can include
items such as system status, remaining capsule energy, capsule
location, capsule orientation, target location, target orientation,
selected mode of operation etc. Further details on
communication/control in preferred embodiments follow.
[0049] An uplink wireless connection (from the capsule to an
external to the body device) can serve multiple purposes and is
often important for ingestible capsule applications. The uplink can
be used for collection of sensed data, such as images/video of an
optical/ultrasound capsule. This communication can eliminate the
need for the collection of the capsule itself, allowing it to be
disposable. The uplink communication can furthermore be used for
collection of other sensed data including but not limited to:
capsule position, orientation, chemical environment properties,
remaining battery lifetime, system status and component
performance, biomarkers such as proteins or DNA, or neural/muscle
electrical activity, etc. In certain embodiments, sensors can be
integrated into the ingestible capsule to monitor the condition of
the body in terms of temperature, heart rate, respiration rate, pH
and the collected data from each sensor can also be sent wirelessly
to an external controller through the uplink. The combination of
these parameters determines the new programmed state of the capsule
in terms of imaging and sensing conditions.
[0050] This information can be then processed externally in a less
resource-limited device and provide user-friendly data to a user or
medical professional. This data can then enable accurate disease
diagnosis in itself or as part of other collected patient data and
diagnostic measurements. Additionally, it can be used for the
issuing of commands to be sent to the capsule, to dynamically
change operational parameters including but not limited to: imaging
transducer delay, imaging focus depth, imaging direction, imaging
frame rate, propulsion pressure/angle of rotation/rotational
velocity, chemical parameter to be sensed, uplink transmitter
output power, uplink data rate, etc. These commands can be
communicated from the external device to the capsule through a
downlink wireless connection, in a similar way the previously
described uplink functions.
[0051] The uplink and downlink wireless connections can further
form a bi-directional, closed loop feedback system. This can enable
automatic capsule parameter control through sensed data, by
performing analysis of the data and finding optimal sets of output
parameters in an external device processor or look-up table, such
that a desired operation of the capsule is tuned to adapt to
changes in the traversed gastrointestinal tract anatomy, and
specifics of physical orientation, position, chemical environment,
user body condition, etc. This closed loop feedback can for example
be used to enhance imaging of a particular body region such as
pancreas for the diagnosis of pancreatic cancer or GI tract wall
for the detection of polyps, once the capsule location and field of
view meets certain predefined conditions, through motion and frame
rate control. In certain embodiments, this closed loop feedback can
enable the specific motion in response to changes in the pH or
specific reactions along the GI tract, for localized drug
treatment. The implementation of such a bi-directional link thus
constitutes a very important system feature to overcome
uncontrollable parameters such as patient to patient variations and
anatomical differences in the gastrointestinal system.
[0052] Communication between the capsule and an external device for
an uplink can be achieved by electromagnetic (EM) radiation in
radio frequencies (RF). In such embodiments, one or more antennas
are included inside or outside the capsule and transmit EM waves
through the body, to be received by one or more antennas external
and in proximity to the body. The antennas are driven by amplifier
circuits as part of transmitter circuits to allow enough power to
be transmitted such that information is received with sufficient
signal to noise ratio (SNR) at the receiver to meet a fidelity
requirement. In certain embodiments the transmitter encodes data
via digital modulation, such as frequency shift keying (FSK), and
the amplifier provides a constant amplitude, varying frequency
waveform generated by oscillator based circuits, that is encoded by
the baseband data, which could be a digital representation of
captured ultrasound or optical images, location/orientation
information, system status and performance information, body
environment physical indicators (temperature, heart rate,
respiration rate), chemical environment (e.g. pH), etc. In some
embodiments, the operation of the transmit circuitry is variably
active and inactive (duty-cycled), and/or time-interleaved with
other capsule operations, including but not limited to imaging,
chemical sensing, chemical sampling, to meet certain data rate
requirements or as part of energy saving schemes. In some
embodiments where collected data by other components of the
capsule, such as the imager, are available at a rate higher than
the possible data rate of the transmitter circuitry, a memory
storage element, such as a RAM (random access memory), or FIFO
(first-in, first-out) element can be used to temporarily buffer the
sampled data until it is ready to be transmitted by the
transmitter.
[0053] Similarly, for downlink communication, between the external
device and the capsule system, the communication may happen by
means of EM radiation through one or more antennas on/in the
capsule and one or more antennas outside/on the body. The
transmitter circuitry on the outside device similarly may include a
power amplifier, data encoder, oscillator based frequency
generators, etc. It may also include a multiple number of antennas
as part of a phased array to focus radiation to the capsule target.
Due to the data rate of downlink commands for biomedical devices
being commonly lower than the data rate of uplink, ultrasound data
transmission which typically possesses a smaller bandwidth can also
be utilized, for a higher link efficiency, thus forming a hybrid
RF/US bi directional link. In embodiments where the capsule already
uses such elements for other applications, e.g. ultrasound imaging
or propulsion, time interleaving schemes can be used to alternately
perform these operations with communication. E.g. use the
ultrasound transducers for 10 ms to transmit a pulse and receive a
scan to form an image, 230 ms for transmitting uplink data, and 10
ms for receiving downlink commands, for a total of 250 ms repeated
throughout system lifetime or until a command to change operational
modes is issued. For downlink communication, similar data encoding
as uplink can be used, with modulation schemes such as amplitude
shift keying (ASK), on off keying (OOK), FSK, etc. The receiver
inside the capsule possesses circuitry to perform data recovery of
commands, interpretation, and depending on the command, execution
of functions such as sensor actuation, system parameter
modification, e.g. rotation, pressure, imaging focus, frame rate,
RF output power, data rate, drug release amount, image slice
selection, chemical parameter to be sensed, etc.
[0054] With a combination of uplink and downlink, closed loop
feedback can be achieved in the following fashion. Periodically/at
desired time intervals, a processing unit/controller in the
external device takes as inputs the received parameters (location,
orientation, etc.) via the uplink. It may then combine these inputs
with predefined inputs from a user/clinician relating to the
operational mode of interest (e.g. `enhanced imaging of pancreas`,
or `power minimization`), and via a function, map the inputs to
outputs in an optimal way. The mapping may occur via look up tables
and predefined relationships between inputs to outputs, or in other
ways including deep learning and neural networks. The outputs
correspond to system parameters to be tuned/changed in the capsule,
(e.g. imaging transducer delay, imaging focus depth, imaging
direction, imaging frame rate, propulsion pressure/angle of
rotation/rotational velocity, drug release amount, chemical
parameter to be sensed, uplink transmitter output power, uplink
data rate) and are transmitted via the downlink. They are then
decoded by the receiver circuitry in the capsule, interpreted and
acted upon to result in a desired function such as `stop movement`,
`rotate capsule`, `release 10 ug of drug`, etc. When errors between
the resulting action and desired action exist, the processing
unit/controller at the external device can infer them from the
inputs resulting from the uplink, and include them in the optimal
output calculation for the next set of outputs. This closed loop
feedback results in dynamically adapting system parameters that
achieve a desired predefined or dynamically redefined outcome
relating to a capsule system operation in the gastrointestinal
tract.
5) Energy Harvesting
[0055] The purpose of harvesting power from sources external to the
capsule is to ease constraints introduced by electrochemical
batteries, which are commonly used for powering electronic
capsules. These constraints include size, weight, biocompatibility,
lifetime and application-specific capabilities of the capsule
system, and together they may significantly limit the clinical
usefulness of conventional capsules.
[0056] Power harvesting can be used to recharge a battery. Current
batteries such as silver oxide batteries require a long time to
charge. However, new breakthroughs such as batteries with organic
contacts have much faster charging times (in the order of seconds),
are environmental friendly as they do not contain harmful heavy
metals, and can be fabricated in small sizes. Other breakthroughs
include Lithium-Sulfur (Li--S) batteries which are reported to have
3-5 times higher capacity than current batteries. This would allow
implementing new features, and/or improve the current
functionalities of the system such as higher frame rate, which
leads to a batter image quality, and more flexibility and torque
during propulsion.
[0057] For a fixed desired lifetime, power harvesting to recharge a
battery allows for a smaller capacity battery to be used inside the
capsule, thereby a) reducing the capsule weight, b) reducing the
capsule dimensions and making it easier to ingest, c) freeing up
space to ease the physical design of other capsule components, e.g.
antenna for wireless communication, actuators, interconnects etc.,
or c) freeing up space to allow for the implementation of
additional features and inclusion of other components, e.g. drug
reservoirs for drug release applications. Alternatively, for a
fixed battery size/capacity, harvesting to recharge the battery can
a) relax the electrical requirements (e.g. peak/average power
dissipation) of the capsule system and subsystems, e.g. imager,
wireless transceiver, etc., b) extend the lifetime of the device
allowing for longer operation and e.g. traversal of a larger
portion of the gastrointestinal tract, or c) allow for the
implementation of additional features that would require additional
power. A particular feature that could be important for achieving
clinical significance in capsule systems is propulsion, and power
harvesting to recharge a battery could be used to make this feature
possible by providing the additional power needed.
[0058] Power harvesting can also be used to eliminate the need for
an electrochemical battery. With a temporary storage mechanism such
a capacitor, continuous or periodic harvesting can similarly a)
reduce the capsule weight, b) reduce the capsule dimensions, c)
free up space to ease the physical design of other components and
allow inclusion of extra components, d) extend the operational
lifetime of the system, all crucial parameters of a capsule system.
Additionally, it can eliminate a major source of toxicity and a
concern of biocompatibility that many capsule systems face.
[0059] Energy harvesting can primarily be achieved through ambient
harvesting, by generating electricity from the surrounding
environment and within the human body, or through wireless power
transfer. The ability to scavenge energy without an external power
unit makes an ambient harvesting approach attractive for long-term
autonomous operation, however with wireless power transfer, higher
power levels can be more consistently and reliably achieved in a
small form factor. A technique to perform wireless power transfer
is via ultrasound waves. For capsule applications ultrasound
powering could have many advantages: The wavelength of ultrasound
traveling in the body is on the order of millimeters for a
frequency range of 1-10 MHz (the speed of sound in tissue is about
1500 m/s), signifying that acoustic energy can be efficiently
focused to specific capsule locations. Additionally, the low
attenuation of human tissue (in the order of 1 dB/(cm MHz)) allows
the power link from transmitter to receiver to be highly efficient
compared to other techniques.
[0060] FIG. 9 schematically shows this approach, where a transducer
or transducer array 904 placed on the skin of patient 902 directs
acoustic energy 906 to capsule 102 which can harvest this energy
with its acoustic transducers.
[0061] Ultrasound powering could be achieved by including one or
more ultrasonic transducers (piezoelectric elements, capacitive
micromachined ultrasonic transducers or other) on the external to
the body device, in contact with the body, transmitting and
beamforming periodically/at predefined time intervals ultrasonic
waves to be received by one or more ultrasonic transducers in or on
the capsule. The capsule circuitry may include a power recovery
chain connected to the receive transducers that rectifies and
regulates the incoming waves, then stores the resulting DC energy
onto a storage element such as a capacitor or battery, which may be
lithium-ion, zinc-oxide, lithium-sulfur for higher charging rate
and capacity, or other types.
[0062] In embodiments where the capsule already includes ultrasonic
elements for imaging/propulsion, the same elements could be used
for wireless harvesting in a time interleaved fashion. Depending on
the desired profile of powering, e.g., continuous powering or
battery recharging, interleaving can be in short, e.g., 500 ms
imaging/propulsion and 500 ms energy harvesting, or long, e.g., 1
hour imaging, 1 hour recharging. The implementation of a circular
transducer array surrounding the capsule as well as a perpendicular
linear array could have the additional benefit of providing
relatively orientation independent harvesting capability, a
fundamental feature for a capsule that is continuously in motion in
the gastrointestinal tract.
6) Photoacoustic or X-Ray Acoustic Imaging
[0063] In addition to ultrasonic imaging, the capsule could also be
capable of performing photoacoustic imaging. Multiple
light-emitting-diodes (LEDs) and/or laser diodes can be located on
the capsule in conjunction with the array being wrapped around its
body. The light from the LEDs will illuminate the tissue,
triggering it to undergo expansion and contraction and ultimately
create ultrasound waves, which will be sensed by the cylindrical
array. This technique will be valuable in detecting the biochemical
nature of the digestive system. For example, cancerous regions emit
a high photoacoustic signal because of the abundance of blood
vessels. Hence, the photoacoustic and the ultrasound data can both
be used to provide a comprehensive picture of the digestive system.
In addition to photoacoustic imaging, the capsule can be used to
perform x-ray acoustic imaging using a source inside the capsule
that transmits X-ray waves into the medium, causing the medium to
experience a change in temperature and emit pressure waves. These
pressure waves can be detected using the transducers on the
exterior of the capsule and processed to render x-ray acoustic
images.
[0064] FIG. 10 shows this concept for both the photoacoustic and
X-ray acoustic cases. Here capsule 102 includes sources 1002
(optical or X-ray) which emit radiation 1004. Absorption of
radiation 1004 in the body leads to acoustic signals 1006 which are
received by transducers 1008 (cylindrical) and 1010 (linear) to
provide photoacoustic imaging or x-ray acoustic imaging according
to the source type employed.
7) Further Options and Variations
[0065] Capsule 102 can also be enhanced with various other
functions. FIG. 11 shows this idea in general, where module 1102 is
added to capsule 102. One option for module 1102 is a therapy
module, which can be configured to provide therapy such as high
intensity focused ultrasound and drug delivery. The ultrasound
transducer on the capsule can be excited via a CW wave to provide
HIFU (high intensity focused ultrasound) at a desired location.
Propulsion techniques (described above) can be used to situate the
transducer at a certain location so that the HIFU is applied at a
region of interest. In addition, closed-loop feedback can be used
to trigger HIFU once a cancerous lesion is detection in the GI
tract. During HIFU, imaging can be done with the same array or a
different array to ensure that the HIFU is being implemented
correctly. In addition, the capsule can also deliver drugs at a
cancerous region. The drug can be placed inside a reservoir within
the capsule and released once a cancer/lesion is detected. The
ultrasound array can be used to facilitate the release of the drug
using cavitation and/or radiation force.
[0066] Another option for module 1102 is a sensor/sampling module,
capable of functions like: fluid sampling, tissue sampling, and
ambient environmental sensing. In addition to the ultrasonic
imaging, the capsule could also operate as a chemistry lab by
integrating other sensors, such as pH sensor, chemical gas sensors
and pressure sensor, inside the capsule or at the surface of the
capsule. At the same time, a MEMS micromotor could also be
integrated in the capsule to control MEMS window and tips movement,
so that the biological samples (tissue sample or liquid sample)
from the patient's GI tract could be acquired and kept inside the
capsule. These samples could be used for future analysis.
* * * * *